Avoid panicking invalid instructions

src/budget_contract.rs

@@ -246,7 +246,7 @@ impl BudgetContract {
     /// * accounts[1] - The contract context.  Once the contract has been completed, the tokens can
     /// be spent from this account .
     pub fn process_transaction(tx: &Transaction, accounts: &mut [Account]) -> () {
-        let instruction = deserialize(&tx.userdata).unwrap();
+        if let Ok(instruction) = deserialize(&tx.userdata) {
             trace!("process_transaction: {:?}", instruction);
             let _ = Self::apply_debits_to_budget_state(tx, accounts, &instruction)
                 .and_then(|_| Self::apply_credits_to_budget_state(tx, accounts, &instruction))
@@ -254,6 +254,9 @@ impl BudgetContract {
                     trace!("saving error {:?}", e);
                     Self::save_error_to_budget_state(e, accounts);
                 });
+        } else {
+            info!("Invalid transaction userdata: {:?}", tx.userdata);
+        }
     }
 
     //TODO the contract needs to provide a "get_balance" introspection call of the userdata
@@ -299,6 +302,27 @@ mod test {
             Err(BudgetError::UserdataTooSmall)
         );
     }
+    #[test]
+    fn test_invalid_instruction() {
+        let mut accounts = vec![
+            Account::new(1, 0, BudgetContract::id()),
+            Account::new(0, 512, BudgetContract::id()),
+        ];
+        let from = Keypair::new();
+        let contract = Keypair::new();
+
+        let tx = Transaction::new_with_userdata(
+            &from,
+            &[contract.pubkey()],
+            BudgetContract::id(),
+            vec![1, 2, 3], // <== garbage instruction
+            Hash::default(),
+            0,
+        );
+        BudgetContract::process_transaction(&tx, &mut accounts);
+
+        // Success if there was no panic...
+    }
 
     #[test]
     fn test_transfer_on_date() {

src/system_contract.rs

@@ -41,7 +41,7 @@ impl SystemContract {
         account.tokens
     }
     pub fn process_transaction(tx: &Transaction, accounts: &mut [Account]) {
-        let syscall: SystemContract = deserialize(&tx.userdata).unwrap();
+        if let Ok(syscall) = deserialize(&tx.userdata) {
             trace!("process_transaction: {:?}", syscall);
             match syscall {
                 SystemContract::CreateAccount {
@@ -75,6 +75,9 @@ impl SystemContract {
                     accounts[1].tokens += tokens;
                 }
             }
+        } else {
+            info!("Invalid transaction userdata: {:?}", tx.userdata);
+        }
     }
 }
 #[cfg(test)]

src/transaction.rs

@@ -49,7 +49,7 @@ impl Transaction {
     /// * `userdata` - The input data that the contract will execute with
     /// * `last_id` - The PoH hash.
     /// * `fee` - The transaction fee.
-    fn new_with_userdata(
+    pub fn new_with_userdata(
         from_keypair: &Keypair,
         transaction_keys: &[Pubkey],
         contract_id: Pubkey,